They go by many names. When Mom made them, they were fettisdagsbullar, or Fat Tuesday buns. In Swedish bakeries they are more commonly called semlor, or Shrove Tuesday buns.
Semlor are a cardamom-spiced wheat bun. The top is cut off. The insides are scooped out and turned into crumbs. The crumbs are then mixed with almond paste and stuffed back into the bun, which is finally topped with whipped cream. Sounds simple, doesn't it? But they are taken very seriously by Swedes from New Year's Day up until Lent. Traditionally eaten on Tuesday, they are available other days too, because they are delicious. The average Swede eats 5 semlor each year.